Ferrous alloy



Patented 7,1934

UNITED STATES maaons ALLOY Ralph P. De Vries. Menan'ds, my.

No Drawing. Application November 13, 1931,

' SerialNo. 574,915 a 6 Claims. My invention relates to ferrous alloys and particularly to alloys of this character havingan extremely high resistance to corrosion, and this application is a continuation in part of my application Serial No. 495,292, filed November 12,

It is generally conceded that a substantial quantity of chromium, in the neighborhood of say 10% to 20%, is necessary to produce a rustless iron or steel. It is well recognized, however, that chromium irons and steels have many inherent characteristics which preclude the application of such alloys to all uses and purposes. If the amount of carbon iskeptextremely low, say from 0.05% to 0.09%, and the chromium ranges from to or higher, the alloy is to a large extent merely a mechanical mixture which requires mechanical working to develop its major physical properties. Thus, for examp'le, the strength of a five-eighths inch round bar may be fairly good, but the strength of a five inch round bar is comparatively poor. Moreover, such an alloy does not lend itself to many mechanical operations which would immensely enhance its field of usefulness. If greater quantitles of carbon are used than above indicated, the alloy gains in strength but loses in rust resistance.

To resist even ordinary atmospheric corrosion to a degree which will warrant its use for ornamental purposes, such as radiator shells, cooking utensils and general architectural applications, the chromiumcontent of suchirons or' steels must be fairly close to 20% with low carbon. When thus made, such. alloys are resistant'to ordinary atmospheric corrosion but lack the me-' chanical and physical properties requisite to their successful use. -With the chromium range of from 15% to 20% considerable quantities .of carbon must be added-" ii the steel is to be hardened, and while hardening generally increases the rust resistance of the alloy, it is manifestly an operation which can not be commercially employed in the above mentioned fields. Thus with a chromium content of 13% to 15%,the alloy can be hardened by the addition of from 0.3% to 0.50% of carbon. If the chromium is increasedto 17%, at least; 0.65% of carbon must be used for hardening. If the chromium content is increased to 20% or better, more than 1% of carbon must be added to the alloy. Such ad-.

but are useless for the architectural. ornamental v and structural purposes above mentioned.

Grain refinement and increase in strength are more or less directly proportional to the amount of carbon in the alloy. Therefore, while it is desirable to use very small quantities of carbon, approximating 0.05%, for the sake of attaining high resistance to rust, it is impossible in such case to obtain the necessary physical characteristics in the alloys. Y

Many attempts have been made to overcome these difllculties by small or large additions of other elements but at the present time, only one of these has been commercially successful to any marked extent. The employment of-substantial 7 quantities of nickel, approximating 10% or more,

in conjunction with high chromium and low carbon contents, has produced alloys capable of being formed or deep drawn, which meet practically all commercial'requirements of workability and 15 many mill difliculties in the fabrication of sheets,

tubes, etc.

For many years it has been known that chromium irons and steels, especially in the non-' hardened state, have great resistance to rusting when the surface is clean, that is free from all oxide and having no scams or defects of any kind. If, however, there exists the slightest seam, break: or discontinuity in the polished surface, corro-,

sion will well up from this defect and spread,

giving an appearance of rust which precludes its .use for many purposes. It has long been known too that many ferrous alloys containing from 10% to 20% of chromium show,'after exposure, to the atmosphere, an appearance of corrosion which does not proceed from any defect such as scams or discontinuity in the surface.

Many theories'have been advanced as to why. such alloys present this appearance of superficial rusting on the polished surfaces when the alloy is apparently immune to substantial attackflby corrosion, and after many years of investigating these phenomena, I am inclinedto believe that the nature of the crystal grains is such that'the appearance of superficial rust proceeds entirely from the boundaries of these crystals, and that the resistance to' rusting depends wholly upon the size, and arrangement of the crystals in. the alloy which partakes more of the nature of a mechanical mixture than of a true chemical solu-' tion. Intergranular corrosion" permits gases, 1 10 particularly those under pressure, to permeate the grain boundaries and thereby destroy the steel. The iron chromium base may be sufiicient to resist the corrosive action of certain gases and liquids, but the interg* lnular permeability of these chromium alloys permits gases to filter around the grain boundaries and, in many instances, reduces the strength of the alloy to such extent that it may be powdered between the fingers.

I find that this appearance of superficial rusting of chromium irons and steels and intergranular corrosion generally, in such alloys may be prevented by small additions of silver, say from 0.03% to 1%. Moreover, the small additions of silver, in many instances endow the alloy with physical characteristics seldom if ever found in alloys containing iron as a principal constituent with chromium.

In addition to silver, I may add to my alloy one or more elements of the group which includes copper, molybdenum, or aluminum in percentages ranging up to about 2% of each; but the total additions-taken together, should not exceed about 3.5%. All of these elements add. to the resistance of my chromium-silver alloy and give it physical characteristics which widen its field of usefulness. Thus, aluminum and copper increase the strength of the alloy at elevated temperatures, while molybdenum adds to the acid resistance, especially with hydrochloric acid in dilute solutions, without detracting in any way from its resistance to atmospheric corrosion.

I prefer to keep the manganese within the ranges usually encountered in steel making practice, that is, from about 0.30% to about 0.75%. Likewise, silicon may be present in the quantities usually encountered or somewhat greater. Phosphorus and sulphur will generally be limited to 0.025% maximum except where the alloy is to encounter many machining operations in which .case the sulphur may be increased to as high The alloy of my invention may be made with carbon as little as can be melted, generally about 0.04%, up to carbon as high as 1.5%. chromium 10% to 25%, silver 0.03% to 1%, and silicon in the quantities ordinarily used in steel making up to 1.25%. To this may be added up to about of alloying elements selected from the group-popper, molybdenum and aluminum in percentages ranging up to 2.0% of each. In other words, my alloy consists essentially of iron, chromium and silver to which other alloying ingredients, amounting to a total maximum of about 5.50%, may be added. This, with the highest carbon permissible, and making no allowancefor impurities, makes a total of about 7%. Hence it is to be understood that the term,

fthe remainder being substantially iron, as used in the claims, is to be taken as meaning iron and .not to exceed about 7% of other alloying ingredients.

The amount of silver that can be successfully alloyed with iron and chromium is comparatively small and, generally speaking, I prefer to use it minute quantities of silver to the fact that its alloying properties, are so extremely. limited.' Thus, the amount of silver that is determined as present in the alloy is no indication of the important function it performs. Silver may be present at the grain boundaries in almost infinitesimal thickness.

It must be manifest that if the corrosion properties of chromium iron and steel are improved by such small additions of elements, and said elements increase the resistance to corrosion at the grain boundaries, they must also have considerable effect upon the mechanical properties of the alloy. This I have found to be so. In stripsteel thick made to the following chemical analysis:

Per cent 0.50 15.88 0.82

Carb n Chromium Silir-nn Copper 0.80 Silver 0.18

I have attained an elongation of 50.2% in two inches and find that the elongation in the two inches, not including the break, is very uniform throughout. This is a characteristic sometimes found in non-ferrous metals but seldom if ever found in alloys containing iron as its principal constituent with carbon. 1

Other good examplesof my alloy are given in the following table, the percentages being by weight:

' %0 %Or as %Cu %Ag. %Al %M0 25%, and silver from 0.03% to under 1%; the

remainder being substantially iron.

2. A ferrous alloy having high resistance to atmospheric corrosion and containing as essential alloying ingredients chromium from 10% to 25%, and silver from about 0.07% to about 0.2%; the remainder being substantially iron.

3. A ferrous alloy having high resistance to atmospheric corrosion and containing chromium from 10% to 25%, silver from0.03% to under 1%, and effective amounts up to 2% of an element selected from the group-copper, molybdenum and aluminum; the remainder being substantially iron.

4. A ferrous alloy having high resistance. to atmospheric corrosion and containing chromium from 10% to 25%, silver from about 0.07% to about 0.2%, and effective amounts up to 2% ob an element selected from the group-copper, 150

from to silver from about 0.07% to molybdenum and aluminum; the remainder being substantially iron.

5. A ferrous alloy having high resistance to atmospheric corrosion and containing chromium 6. A ferrous alloy having high resistance to I atmospheric corrosion and containing chromium from 10% to 25%, silver from 0.03% to under 1%, and efl'ective amounts up to 3.5% of elements about 0.2%, and efiective amounts up to 3.5% of elements selected from the groupcopper, molybdenum and aluminum; the quantity of any one element of the group not exceeding about 2%;

and aluminum; the quantity of any one element of the group not exceeding about 2%; the remainder being substantially iron.

RALPH P. DE VRIES.

the remainder being substantially iron.

CERTIFICATE OF CORRECTION.

0 .Patent No. 1,969,705. August 7, 1934.

RALPH P. DeVR IES. 5

It ishcreby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 93, for "0.50" read 0.05; and that the said LettersPa'tent should be read with this cor- 0 rection therein that the same may conform to'the record of the case in the Patent Office.

Signed and sealed this 11th day of September, A. D. 1934.

Lesiie Frazer Acting Commissioner oi Patents.

(Seat) 7 selected from the group-copper, molybdenum. 80

from to silver from about 0.07% to molybdenum and aluminum; the remainder being substantially iron.

5. A ferrous alloy having high resistance to atmospheric corrosion and containing chromium 6. A ferrous alloy having high resistance to I atmospheric corrosion and containing chromium from 10% to 25%, silver from 0.03% to under 1%, and efl'ective amounts up to 3.5% of elements about 0.2%, and efiective amounts up to 3.5% of elements selected from the groupcopper, molybdenum and aluminum; the quantity of any one element of the group not exceeding about 2%;

and aluminum; the quantity of any one element of the group not exceeding about 2%; the remainder being substantially iron.

RALPH P. DE VRIES.

the remainder being substantially iron.

CERTIFICATE OF CORRECTION.

0 .Patent No. 1,969,705. August 7, 1934.

RALPH P. DeVR IES. 5

It ishcreby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 93, for "0.50" read 0.05; and that the said LettersPa'tent should be read with this cor- 0 rection therein that the same may conform to'the record of the case in the Patent Office.

Signed and sealed this 11th day of September, A. D. 1934.

Lesiie Frazer Acting Commissioner oi Patents.

(Seat) 7 selected from the group-copper, molybdenum. 80 

